Scientists say the plume is condensed seawater that's laced with hydrochloric acid and glass particles that form when lava interacts with seawater.
In response to the laze threat, U.S. Geological Survey scientist Wendy Stovall told residents that "if you're feeling stinging on your skin, go inside".
That's producing laze, a risky mix of lava and haze, which is adding to the ongoing challenges.
Ash fall has seen more than a quarter inch of ash covering much of the surrounding region, with trade winds blowing the cloud out to other areas of the island.
The laze plumes can travel with the wind and change direction at any time, Hawaii County Civil Defense advised. "Getting too close to the lava can result in serious injury or death", Lt. Cmdr. (His was the first reported injury from this month's eruptions.) Now, as lava pours into the ocean, officials have begun issuing warnings about the resulting "laze", unsafe plumes of hydrochloric acid, steam, and glass particles. Even a wisp can cause eye and respiratory irritation, and it causes acid rain that has corrosive properties equivalent to diluted battery acid, the U.S. Geological Survey said.
The US Coast Guard has enforced a safety zone extending 300 metres from where the lava has entered the ocean.
Joseph Kekedi, an orchid grower who lives and works about 3 miles from where lava dropped into the sea, said luckily the flow didn't head toward him.
"Like typical eruptions and lava flows, it's really allowing Madam Pele to run its course", he said, referring to the Hawaiian goddess of volcanoes and fire.
Twitter USGSThis USGS map shows the current activity and lava flows and where the lava is meeting the ocean
The rate of sulphur dioxide gas shooting from the ground fissures tripled, leading Hawaii County to repeat warnings about air quality.
Video shot Monday shows lava spewing high into the air from the Kilauea volcano.
As Hawaii's Kīlauea volcano continues to erupt, lava flows have reached the Pacific Ocean, prompting local authorities to issue warnings of a potentially deadly new hazard.
Thousands of Big Island residents who were living near the lava flows have already evacuated.
The Kilauea volcano has sent oozing lava and noxious gas into neighbourhoods for more than two weeks, burning homes, driving out residents and producing explosive eruptions at the summit.
The saga of a Hawaii volcano's impact on rural communities is heading into its third week.
Lava flows have sped up as fresher magma mixes with decades-old magma, creating hotter and more fluid flows, scientists said. A few people were temporarily trapped when a flow crossed a road.
So far lava from the volcano has destroyed over 40 homes and buildings, and geologists are anxious that magma - lava that hasn't yet reached the surface - running underground could reach areas up to 40 kilometers (25 miles) east of the volcano itself, causing further destruction.